Learn about objective 2 of the polio endgame

Objective 2

In May 2012 the World Health Assembly declared the completion of poliovirus eradication to be a programmatic emergency for global public health and called for a comprehensive polio endgame strategy. In response, the Polio Eradication and Endgame Strategic Plan 2013-2018 was developed.

The plan outlines a comprehensive approach for completing eradication including the elimination of all polio disease (both wild and vaccine-related).

IPV introduction

The endgame plan calls for the introduction of IPV in all OPV-only using countries by the end of 2015. The primary role of IPV will be to boost population immunity against type 2 polio virus before removing OPV type 2 globally. More specifically, IPV needs to be introduced for the following reasons:

• To reduce risks. Once OPV type 2 is withdrawn globally, IPV will help fill the immunity gap by priming population against type 2 polio virus should it be reintroduced. A region immunized with IPV would have a lower risk of re-emergence or reintroduction of wild or vaccine-derived type 2 polio virus.

• To interrupt transmission in the case of outbreaks. Should monovalent OPV type 2 (mOPV type 2) be needed to control an outbreak, those primed with IPV would be expected to have a better immune response, thus facilitating outbreak control and interruption of polio transmission.

• To hasten eradication. IPV will boost immunity against poliovirus types 1 and 3 in children who have previously received OPV, which could further hasten the eradication of these two wild viruses.

OPV type 2 withdrawal

There are three types of wild poliovirus (WPV) - type 1 (WPV1), type 2 (WPV2) and type 3 (WPV3) - each of which is targeted by a different component of the trivalent oral polio vaccine (tOPV).
Live attenuated vaccines are effective against the wild virus, but in very rare cases can lead to paralysis. There are two ways this can occur:

• Vaccine Associated Paralytic Poliomyelitis (VAPP): for every birth cohort of 1 million children in OPV-only using countries, there are 2-4 cases of VAPP. This translates to an estimated 250 – 500 VAPP cases globally per year. Of these, about 40% are caused by OPV’s type 2 component.

• Circulating Vaccine Derived Poliovirus (cVDPV) outbreaks: these rare outbreaks occur when a vaccine-related virus is passed from person-to-person, mutating along the way and acquiring wild virus transmissibility and neurovirulence characteristics. Almost all cVDPV outbreaks in recent years have been caused by a type 2 vaccine-derived virus.

Although wild polio virus type 2 appears to have been eradicated globally in 1999, vaccine-related type 2 viruses continue to cause the majority of cVDPV outbreaks and many VAPP cases. Therefore, OPV type 2 now carries more risk than benefit and undermines global polio eradication efforts. This is why it will be replaced with bivalent OPV (bOPV) vaccine, which will continue to target the remaining polio types, WPV1 and WPV3. Once these types are eradicated, bOPV will also be withdrawn.

Routine immunization strengthening

For the right reasons, much of the polio eradication efforts previously focused on campaigns. However, in the endgame, routine immunization and polio eradication can no longer occur independently.

The central reason for strengthening routine immunization is to achieve and maintain high population immunity against polioviruses, especially type 2 after OPV2 is withdrawn. The number and length of both WPV and cVDPV outbreaks are closely correlated with weaknesses in routine immunization systems.

This is also a golden opportunity to strengthen systems in some of the countries with the lowest routine immunization coverage levels and offer immediate and direct benefits to countries. Many of the polio eradication efforts in country can contribute to the strengthening of routine immunization to further enhance the delivery of vaccines through human resources, tracking of target populations, training venues and systems, monitoring strategies for improving coverage and monitoring and evaluation efforts.

This is already occurring in Africa and India, where substantial portions of the Global Polio Eradication Initiative (GPEI) efforts support routine immunization. The partnership between GPEI, the GAVI Alliance and other partners further provides an opportunity to strengthen routine immunization through improved planning, technical assistance and accountability.